Magnetostrictive relay



United States Patent MAGNETOSTRICTIVE RELAY Walter Grant Leslie and Daniel T. Gundersen, Chicago, Ill., assignors to Cook Electric Company, Chicago, 111., a corporation of Illinois Application January 11, 1952, Serial No. 265,984

4 Claims. (Cl. 20087) This invention relates to circuit control devices, and more particularly to electrical'switches which are actuated by the influence of an electromagnetic field.

It is an object of this invention to utilize the magnetostrictive properties of magnetic materials in an improved switch mechanism which will be characterized by rapid, positive operation.

Magnetic circuit control switches heretofore known in the art have generally utilized only the principle of magnetic attraction to cause the motion necessary to complete a circuit. In order to build a switch actuated by magnetic attraction which will operate on small current or power requirements, it is necessary that it have extremely small contacts and a delicate mechanism which is fragile and readily damaged by vibration or rough use. To build a relay or magnetic switch with the durable construction necessary for most mobile uses requires a heavy armature and contact assembly and consequently a large power input to the actuating coil for positive operation. One of the results of this power requirement is usually a slow operating relay actuated by marginal power.

Accordingly, it is an object of this invention to employ the magnetostrictive principle in an electromagnetic switch which will be durable in all types of service but still capable of rapid operation with low power input.

It is a further object of this invention to increase the speed of operation of electromagnetic switches by utilizing a bimetallic sheet material in which the two constituent metals have coefficients of magnetostrictive elongation of opposite sign.

Another object of this invention is to make an improved relay which utilizes both the principles of magnetic attraction and magneltostriction in a manner which will cause more rapid, positive action of the control elements on a smaller power requirement than heretofore.

An additional object of this invention is to create a relay which will be useful over a wider range of frequencies than heretofore known. The customary relay is designed for operation on the normal power frequencies and will be unsatisfactory at higher frequencies as a result of excessive iron losses. A device constructed following the teaching of this invention will reduce this disadvantage without loss of sensitivity or speed of operation. Such a relay is ideally suited for aircraft uses where the power sources usually supply a voltage of higher frequency to conserve weight.

It is an additional object of this invention to provide a magnetostrictive circuit control device which will be compensated for changes in ambient temperature which might otherwise produce erratic cont-r01 characteristics.

Further and additional objects of the invention will appear from the description, accompanying drawings, and appended claims.

The magnetostrictive phenomenon is a magnetomechanical efiect wherein the physical dimensions of certain materials are changed for'a change in the magnetic 2,764,647 Patented Sept. 25, 1956 flux present in the material. It has been observed that pure nickel contracts in a magnetic field, pure iron first elongates and then contracts and many alloys such as iron-nickel or iron-cobalt alloys elongate in a field.

In carrying out this invention, the principle of magnetostriction is utilized by bonding two metal strips together, one having a positive coefiicient of magnetostriction and the second a negative coetficient of magnetostriction, that is, one elongates and the second contracts in a magnetic field, and thus a bimetal is formed which will assume an arcuate shape in a magnetic field.

In carrying out this invention in one form, a relatively long narrow strip of magnetostrictive bimetallic sheet material is provided. More specifically, a bimetallic strip is secured as a cantilever beam within a hollow coil of insulated wire. A resilient magnetic strip is mounted at the opposite end of the coil with its free end Within the coil and positioned relative to the free end of the bimetallic strip. Upon energizing the coil, the magnetostrictive character of the bimetal will cause it to assume an arcuate shape and move toward the second strip of magnetic material. This motion will be augmented by the magnetic attraction of the two free ends which will have assumed opposite magnetic polarities. Thus the additive character of the magnetostrictive effect and the magnetic attraction will produce a quick action on less power than was heretofore possible. It has been found that the ratio of thickness of the two sheet materials composing the bimetallic member should be close to unity for maximum displacement of the free end of the bimetallic members. It has also been found that the thickness of the bimetallic member determines its over-all displacement, and a thickness should be chosen of the minimum required for rigidity suflicient to prevent erratic operation.

Another form of this invention utilizes a concave disc of two magnetostrictive materials having magnetostrictive coeflicients of opposite sign. This disc is mounted on the core of an electromagnetic device in such a manner that a radial magnetic field is created in the disc when the electromagnet is energized. When flux density due to this field becomes sufiicient, a sudden snapping motion is produced in the disc causing it to distort from the concave to a convex position. This sudden snapping motion is used to close a pair of electrical contacts which are supported in a position relative to the disc. As long as the electromagnet is energized, the disc will remain in its distorted position producing a firm, positive contact of low impedance. Immediately upon de-energizing the electromagnet, the disc will snap back to its original undistorted position providing a quick, positive circuit break which will minimize contact arcing and consequent burning, pitting and general contact deterioration.

For a more complete understanding of the invention, reference should now be made to the accompanying drawings wherein:

Figure 1 is a front elevation in section illustrating one embodiment of the invention;

Fig. 2 shows a second embodiment of the invention, also illustrated in section, which utilizes a disc type of magnetostrictive element;

Fig. 3 is a partial section taken along line 3-3 of Fig. 2 and shows the contact orientation on the bimetallic disc;

Fig. 4 shows another embodiment of the invention, also in section, which is characterized by increased sensitivity resulting from the use of two bimetallic strips; and

Fig. 5 is a front elevation in section of an embodiment utilizing the combination of two bimetallic elements and the principles of magnetic attraction.

Referring now to the drawings and more particularly to Fig. 1, indicates a relay constructed in accordance with this invention. A coil 11 is wound on a hollow insulating core 12 having end members 13 and 14. Fixed at one end of this hollow insulating core is a supporting disc 15 of insulating material. adapted to rigidly support bimetallic member 16. Bimetallic member 16 is composed of two metals having magnetostrictive coefficients of opposite sign such as nickel and iron-cobalt. .Metal 46 has a negative magnetostrictive coetficient such as nickel and metal 48, bonded thereto, has a positive coeflicient such as iron-cobalt alloy so that the member will assume an arcuate shape when in a magnetic field. It has been found that by bonding together a strip of nickel and a strip of an iron-cobalt alloy having the same thermal coefiicient as nickel, a bimetallic element results which will be responsive to changes in magnetic field but will show little effect due to changes in ambient temperature. A desirable alloy for this purpose is one composed of 60% iron and 40% cobalt. Upon the free end of bimetallic member 16, two contact members 17 and 13, preferably of precious metal, are attached.

Coil 11 is closed at its other end by a disc 19, also of insulating material. Secured in disc 19 are contact member 20 having contact 22 secured thereto and contact member 21 with contact 23 fixed thereto. Contact member 21) provides a normally closed circuit with the bimetallic contact member 16 through contacts 18 and 22 while contact member 21 provides a normally open circuit with respect to contact member 16. In this embodiment contact member 20 is made of a material which is nonmagnetic such as copper or brass, while contact member 21 is composed of some magnetic material such as soft iron. Secured in supporting disc 15 is a spring member 24 having an adjusting screw 25 threaded into its free end. This spring 24 is adapted to tension bimetallic member 16 to determine the current in coil 11 which will be sufficient to cause the motion necessary to complete a circuit through contacts 17 and 23. Also inserted in supporting disc 15 are two metallic inserts 26 and 27. These inserts are chosen according to their thermal coefiicients of expansion so that any thermal effects which do exist in the bimetallic member 16 can be compensated for by expansion or contraction of metallic inserts 26 and 27. This results in a lateral motion of bimetallic member 16 in the base 15, and compensates for thermal distortion in the bimetal. The manner in which this relay operates will now be briefly described.

The normal position for bimetallic member 16 is in contact with normally closed contact member 20 through contacts 18 and 22. When current of sufficient magnitude flows in coil 11, the bimetallic member will assume an arcuate shape as indicated by the dotted lines of Fig. l which will cause contacts 22 and 18 to disengage and contact 17 to approach contact 23. As contact member 21 and the bimetallic member 16 are both composed of magnetic materials under the influence of a magnetic field resulting from the current in coil 11, member 21 will assume a magnetic polarity at its free end and bimetallic member 16 will assume an opposite magnetic polarity at its free end. These members will therefore be magnetically attracted which will augment the motion of contact 17 toward contact 23 resulting from the magnetostrictive distortion of bimetallic member 16 caused by the magnetic field in the hollow core. As the magnetostrictive effect is almost instantaneous this motion and consequently the relays operating characteristics will be very rapid and positive. Adjusting screw 25 can be turned to adjust spring 24 and thus determine at what current in coil 11 contact 17 will engage contact 23.

Another embodiment of the invention based on the same principle uses a disc-shaped moving element. This embodiment of the invention is illustrated in Figs. 2 and 3 and has the characteristic of very rapid, positive operation resulting from a snap action. In the relay 50, an electromagnetic coil 23 of insulated wire is wound upon an iron core 29 and enclosed in a soft iron case 30. Core 29 and case 30 provide a low reluctance magnetic path for the flux resulting from current in coil 28. Mounted on the open end of core 29 is a bimetallic disc 32 displaced from the core 29 by an insulating spacer 33 and secured thereto by attaching means such as screw 34. Screw 34 is electrically insulated from disc 32 by an insulator 40. The bimetallic disc 32 is composed of metals having magneto+ strictive coefiicients of opposite sign as described above. In this embodiment, metal 35 is an iron-cobalt alloy and member 36 is composed of nickel. As shown in Fig. 3, electrical contacts 37, preferably of precious metal, are secured to the periphery of disc 32. These contacts 37 are adapted to engage normally closed contacts 38 or normally open contacts 39. Normally closed contacts 38 are mounted upon insulating spacer 41 and normally open contacts 39 are secured in a base 42 of a nonmagnetic and electrically insulating material which also acts as a closure for the soft iron case 30, thus sealing the entire structure.

The manner in which this embodiment operates is similar to the embodiment of Fig. 1. When a current flows in coil 28, a magnetic field is induced in core 29 which traverses bimetallic element 32 and the soft iron case 30. The flux in disc 32 causes an elongation of the iron-cobalt alloy 35 and a contraction of the nickel element 36. When the flux in disc 32 reaches some predetermined magnitude, a sudden inversion of the disc is caused so that instead of its normal concave shape it will now assume a convex configuration at the same time completing a circuit through contacts 37-37 and 39-39.

An embodiment similar to that shown in Fig. 1 is indicated by numeral 43 of Fig. 4. This embodiment is characterized by greater sensitivity resulting from the multiplied motion of two bimetallic strips. Here, coil 11 is wound on a hollow insulating core 12 having end members 13 and 14. Secured in an insulating supporting disc 15 are two bimetallic members 16 and 44. Bimetallic member 16 has spring 24 and adjusting screw 25 associated therewith as in the embodiment of Fig. 1. Secured to bimetallic member 16 are contacts 17 and 18, and secured to bimetallic member 44 is contact 45. An insulating end closure member 19 is secured to the other end of coil 11 and supports contact member 20 having contact 22 secured thereto. The bimetallic members 16 and 44 are so oriented that under the influence of a magnetic field, their effects will be additive, thus increasing the sensitivity of the relay. In order that this additive character exists, metal elements 46 and 47 are the elements having the negative magnetostrictive coeflicient such as nickel, and elements 48 and 49 have the positive coeflicient such as the iron-cobalt alloy. Thus, when a magnetic field is present in the hollow core, bimetallic members 16 and 44 will assume arcuate shapes as illustrated by the dotted lines in Fig. 4. This will complete an electrical circuit between conductors 51 and 52 through bimetallic member 16, contact 17, contact 45, and bimetallic member 44, and open the normally closed electrical circuit between conductors 51 and 53.

In Fig. 5, the advantages of magnetic attraction described above in conjunction with Fig. l are utilized while at the same time gaining the advantages of two bimetallic elements illustrated in the embodiment of Fig. 4. Relay 54 consists of a coil of insulated wire 11 wound upon a hollow insulating core 12 as in the previous embodiments. One end of the hollow core is closed by an insulating supporting disc 15 which has imbedded therein a bimetallic member 16 having contacts 17 and 18 secured thereto and a resilient adjusting means 24 with adjusting screw 25 threaded thereto. The other end of the hollow insulating core 12 is closed by insulating disc 55 which supports an additional bimetallic member 56 having contact 63 fixed to thefreeend thereof. Disc 55 also supports a nonmagnetic contact member 20 having a contact 22 secured thereto. This whole unit is then sealed by end closures 57 and 58. Fig. shows this embodiment in the unactuated position, which means that no current is flowing in coil 11. When current flows in coil 11, a magnetic field is induced within the core 12 and the bimetallic elements 16 and 56 are distorted thereby. Bimetallic element 16 consists of metal 48 having a positive magnetostrictive coefficient and metal 46 having a negative magnetostrictive coefficient. Bimetallic member 56 is composed of metallic strip 59 having a negative magnetostrictive coefficient and 61 having a positive magnetostrictive coeficient. Therefore, as the magnetic flux within hollow core 12 increases, the bimetallic members 16 and 56 will assume the positions shown by the dotted lines in Fig. 5. This will open a circuit between conductors 51 and 53 and will complete a circuit between conductors 51 and 62 through bimetallic member 16, contact 17, contact 63, and bimetallic member 56. Again, this motion will be practically instantaneous as the magnetostrictive effect is a substantially instantaneous phenomenon and will therefore characterize this relay by rapid, positive operation. Additionally, as both members 56 and 16 are of magnetic materials, they will more positively engage one another as a result of the magnetic attraction which the free ends thereof possess when a field is present within core 12. It will thus be seen that a relay has been provided which will combine the advantages of several known magnetic phenomenon. The magnetostrictive effect on a bimetallic element and the magnetic attraction of contact members within a magnetic field have been combined to give an improved quick-acting relay.

Other modifications and embodiments of this invention will be immediately apparent to one skilled in the art. Many various contact arrangements become immediately apparent as well as the possibility of improved operation by the addition of various iron flux paths to reduce the over-all reluctance of the magnetic path. The normally closed contacts may also be of a magnetic material to give a quick break. As the bimetallic contact member under the influence of a magnetic field moves away from the normally closed contact member, the magnetic attraction would tend to maintain the closure until the magnetic force is insufficient and at that point the contacts will disengage Very rapidly. Also, it is possible to utilize other magnetic materials besides the nickel and iron-cobalt alloy mentioned herein without departing from the invention. It also might be desired to completely evacuate the structure of this invention or to impregnate it with some electrically inert atmosphere.

Thus, this invention provides a relay which will be extremely rapid in operation and have contact closure which is positive and free from chatter. The relay will be responsive to voltages over a wide range of frequency and will not be detrimentally affected by changes in ambient temperature.

Without further elaboration, the foregoing will so fully explain the gist of our invention that others may, by applying current knowledge, readily adapt the same for use under varying conditions of service, without eliminating certain features, which may properly be said to constitute the essential items of novelty involved, which items are intended to be defined and secured to us by the following claims.

We claim:

1. A control device for controlling electric circuits comprising a contact member composed of two elongated magnetostrictive strips having different coeflicients of elongation and bonded together so that said member will assume a deformed position when in a magnetic field, a resilient contact member composed of magnetically attractable material, said contact member and resilient contact member being mounted as cantilever beams having free ends supported in overlapping spaced relation, and means for longitudinally magnetizing said contact member and resilient contact member to effect actuation thereof due to the combined magnetostrictive deformation of said contact member and the attractive force between said contact member and said resilient contact member.

2. A control device for controlling electric circuits comprising a contact member composed of two elongated magnetostrictive strips having different coefficients of elongation and bonded together so that said member will assume a deformed position when in a magnetic field, a resilient contact member composed of magnetically attractable material, said contact member and resilient contact member being mounted as cantilever beams having free ends supported in overlapping spaced relation, and an elongate hollow coil of insulated conducting material surrounding said contact member and resilient contact member creating a magnetic flux in said contact member and resilient member to effect actuation thereof due to the combined magnetostrictive deformation of said contact member and the attractive force between said contact member and resilient contact member.

3. A control device for controlling electric circuits comprising a contact member composed of two elongated magnetostrictive strips having different coeificients of elongation and bonded together so that said member will assume a deformed position when in a magnetic field, a resilient contact member composed of magnetically attractable material, said contact member and resilient contact member being mounted as cantilever beams having free ends supported in overlapping spaced relation, means for longitudinally magnetizing said contact member and resilient contact member to effect actuation thereof due to the combined magnetostrictive deformation of said contact member and the attractive force between said resilient contact member and said contact member, and tensioning means for said contact members whereby the magnetic field required for actuation of the control device may be predetermined.

4. A control device for controlling electric circuits comprising a contact member composed of two elongated magnetostrictive strips having different coefficients of elongation and bonded together so that said member will assume a deformed position when in a magnetic field, a resilient contact member composed of magnetically attractable material, said contact member and resilient contact member being mounted as cantilever beams having free ends supported in overlapping spaced relation, an elongate hollow coil of insulated conducting material surrounding said resilient contact member and said contact member creating a magnetic flux in said contact member and resilient member to effect actuation thereof due to the combined magnetostrictive deformation of said contact member and the attractive force between said contact member and said resilient contact member, and tensioning means for said contact members whereby the magnetic flux required for actuation of the control device may be predetermined.

References Cited in the file of this patent UNITED STATES PATENTS 1,272,402 Egerton July 16, 1918 2,030,101 De Lanty Feb. 11, 1936 2,207,601 Shakespeare et al. July 9, 1940 2,264,022 Ellwood Nov. 25, 1941 2,264,746 Ellwood Dec. 2, 1941 2,286,800 Gustin June 16, 1942 2,475,148 Massa July 5, 1949 2,487,052 Hastings Nov. 8, 1949 2,491,907 Reifel et a1. Dec. 20, 1949 FOREIGN PATENTS 495,657 Germany Apr. 10, 1930 538,476 Germany Nov. 14, 1931 

